From OPeNDAP Documentation

This is the OPeNDAP 4 Data Server, also known as Hyrax. See our new Hyrax Installation and Configuration Guide.

Note: The documentation on this is somewhat out of date as of October 2017.

This page leads you through implementing and configuring Hyrax. Work through this page from top to bottom.

Hyrax Operational Overview


Hyrax uses the Java servlet mechanism to hand off requests from a general web daemon to DAP format-specific software. This results in higher performance for small requests. The servlet front end, which we call the OPeNDAP Lightweight Front end Server (OLFS) looks at each request and formulates a query to a second server (which may or may not on the same machine as the OLFS) called the Back End Server (BES).

The BES is the high-performance server software from HAO. It handles reading data from the data stores and returning DAP-compliant responses to the OLFS. In turn, the OLFS may pass these response back to the requestor with little or no modification or it may use them to build more complex responses. The nature of the Inter Process Communication (IPC) between the OLFS and BES is such that they should both be on the same machine or be able to communicate over a very high bandwidth channel.

Both the OLFS and the BES will run and serve test data immediately after a default installation. Additional configuration is required for them to serve site specific data.

Hyrax Features
THREDDS Catalog Support Hyrax supports the THREDDS catalogs. It can serve user supplied static catalogs and it will dynamically generate THREDDS catalogs of it's internal holdings.
Dataset Aggregation Collections of related data resources can be collected into a single dataset using the aggregation features. Typically these are formed for geographic tiles, time series, etc.
Adding/modifying dataset content Datasets can be modified by the server without having to actually change the underlying files. These views are independently accessible from the original data. Both dataset metadata and data values may be added or changed.
Multiple source data formats Server can ingest source data stored as HDF4, HDF4-EOS, HDF5, HDF5-EOS, NetCDF-3, NetCDF-4, CEDAR, FITS, Comma Separated Values, and raw ASCII and Binary formats. Because of Hyrax's extensible design, it's easy to add new source data formats.
Multiple Return Formats For Data rRetrieval in multiple return formats Hyrax is able to return data in DAP, DAP4, NetCDF-3, NetCDF-4, JSON, CSV, and ASCII formats, Or, you can add your own response types.
Gateway Service Hyrax supports a gateway service feature that allows it to provide DAP (and other Hyrax) services for remotely held datasets that are stored in any of Hyrax's source data formats.
RDF Hyrax provides RDF descriptions of it's data holdings. These can enable semantic web tools to operate upon the metadata content held in the server.
Server side functions Hyrax supports a number of server side functions out of the box including (but not limited to):
  • geogrid: Subset applicable DAP Grids using latitude and longitude values.
  • grid: Subset any DAP Grid object using the values of it's map vectors.
  • linear_scale: Apply a linear equation to the data returned, including automatic use of CF attributes.
  • version: The version function provides a list of the server-side processing functions available.
  • New ones are easy to add.
Extensible WebStart functionality for data clients Hyrax provides WebStart functionality for a number of Java based DAP clients. It's simple to add new clients to the list that Hyrax supports.
Extensible WebStart functionality for data clients Hyrax provides WebStart functionality for a number of Java based DAP clients. It's simple to add new clients to the list that Hyrax supports.
Extensible/Configurable web interface The web interface for both Hyrax and the administrator's interface can be customized using CSS and XSL. You can add your organizations logo and specialize the colors and fonts in the presentation of data sets.
Administrator's interface Control and dynamically update Hyrax from a convenient web interface. See the Admin interface documentation.
WMS services Hyrax now supports WMS services via integration with ncWMS.
JSON responses Both metadata and data are now available in a JSON encoding.
JSON responses Both metadata and data are now available in a JSON encoding.
w10n Hyrax comes with a complete w10n service stack. W10n navigation is supported through the default catalog where all datasets and "structure" variables appear as graph nodes. Data can be acquired for atomic types or arrays of atomic types in a number of formats.
Feature Request
Is there a feature you would like to see but don't? Let us know: support@opendap.org or opendap-tech@opendap.org (You need to subscribe first)

Downloading and Installing

The download and installation instructions are kept together. For the latest release look at the Hyrax downloads page.

Building And Installing From Source

Getting and Building The Code From GitHub

Server Configuration

At this point, you should have a running Hyrax server, but it will not be configured for your needs. In this section you will configure your Hyrax server. To do this, you will need to configure BES and OLFS; optionally, you can configure THREDDS catalogs to provide a custom virtual view of the servers holdings.

Apache Integration

This is an optional step after configuring BES and OLFS. Integrating Hyrax with Apache allows you to integrate your Hyrax server with existing web infrastructure and is the recommended path for enabling user authentication and authorization.

User Authentication

And then there's more...

  • Customizing Hyrax. Here you will find instructions on how to change the colors, fonts, and logo images presented in the Hyrax web pages.
  • System Administrators Workshop Here are slides from a system administrators workshop we gave to the Australian BOM on how to manage a Hyrax instance.
  • Hyrax - Administrators Interface Here are the instruction for using the Hyrax Admin Interface, a web UI that allows one to view logs, restart, reconfigure, and otherwise fiddle with a Hyrax instance.


Hyrax has a number of modules that provide the actual functionality of the server: Reading data files, building different kinds of responses and performing different kinds of server processing operations. Most of these modules work with the BES but some are part of the front (web facing) part of the server.

BES modules

Additional Java Modules that use the BES


Technical Support

Technical Support:

Hyrax Java Development:

  • ndp <at> opendap <dot> org

Hyrax C++ Development:

  • pwest <at> ucar <dot> edu (bes)
  • jgallagher <at> opendap <dot> org (libdap)


OPeNDAP Hyrax development is sponsored by:

Nasa-logo.jpg National Aeronautics and Space Administration

Nsf-logo.png National Science Foundation

This material is based on work supported by the National Science Foundation under Grant No. 0430822. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).

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